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Amstrad 6128 plus CPC 6128 plus does not start

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Hi folks.

I'm new to this forum - and have been quite happy to see all the information on this site. A CPC464 was my first computer about ... 30?! years ago.
I have considered for some time to get a 6128 plus now, for I wanted one with a built in disk, and also sprites support etc. Now, I finally found one that I could collect in person :-)

Bad news: It doesn't boot from its ROM. And I was wondering, whether anyone here could tell from its behaviour, whether the problem might be in the ROM cartridge (i.e.: easily curable), or in the large onboard ASIC (i.e.: non curable), or something in between (i.e.: curable, with some work).


Well, it didn't look too clean from outside. After wiping a layer of dirt off, I thought I'd better look inside - and found the leftovers of numerous bugs (think: hundreds). All these parts wouldn't stick to the printed circuit boards so much, but to the bottom plastic, to the horizontal metal layers of the disk drive etc. (Somewhat disgusting, sorry.) I didn't make a notice in the machine logbook, but gave the machine some emergency cleaning. The floppy belt is also unusable, but I expected that and I don't mind.

The machine came with the burning rubber / locomotive basic ROM.

I've made a CPC 6128 Plus to SCART cable and connected it to an Amiga monitor. Signal injection from Multimeter to the Audio L and Audio R pins on the CPC end makes the monitor emit the beep, and Signal injection from Multimeter to the R, G, B pins makes coloured stuff appear on the monitor - and switching the computer on (supplied with 5 Volts from a laboratory power supply that does *not* reach its current limitation) makes the black monitor image change into a black image with a very light regular scanline/retrace pattern, and also a very high pitched just audible beep comes from the monitor (most of the time, i.e. when the machine appears to start in some way).

Ah, and the power light is on, of course.

Also, when this change in black screen and audible audio occurs, the multimeter shows some 100 kHz up to 4 MHz at the Pins of several ICs, including the CPU, and the ROM socket. So I'm relatively sure, that the CPU runs (in some way), but the machine either fails to initialize the video IC (or program some other internal registers) completely, or the ROM has a problem, or ... something in between.

Now my actual question: Has anybody seen the same behaviour already?

May I just get another ROM cartridge, and hope it would start then?

Or is this a typical behaviour after the internal big Amstrad-ASIC has been killed, which I probably can't replace (it's large, custom, SMD...).

I can do further diagnostics to quite some level, I can also find defective 74xx ICs etc. - but before I start out doing that work, I thought I'd rather ask. (And it may be months or years before I find the time to do it).

Another question (the scanned user manual available somewhere was not too detailed here due to missing images): I read somewhere that the built in floppy drive might live w/o an extra 12 V power supply. I also found in the service manual what looks like a weird construction, where some second 7405 relative is put on top of the 5V line of another one, to derive some 10 V distance in total. Well, I've not looked there in detail and might shake my head in wonders when I do (about the BWLers vs. engineers thing) - but until then: could you tell me if it's really true that the machine needs only one 5 V input?

Ok. I say thank you to all of you for reading this, and thanks in advance for any response.

Kindest regards - flufduff :-)

 :) :) :)

Hello all again :-)

Given I'm still curious, I thought I'd try it again - after all the machine had two days or so to dry, just in case there should be some water left.

It produced the same results. And I forgot to mention: Same dark screen image with or without ROM cartridge inserted.

So... I opened the cartridge, found it basically good looking (no bugs there), but just possibly a bit of damp on two leads. i cleaned all the leads quickly/coarsely with a screwdriver, inserted the ROM PCB, gave it a new cup of tea - no, I mean, switched it on, and - flups - really...? - as I've been used to so often, the very faint sound of a CPC booting, now from the monitor, blue and yellow, and while I was still looking in astonishment and happiness - the cartridge game, sound and colours nice and bright & sharp :-)

All perfect now. And yes, it was the ROM cartridge - or the contacts in the ROM slot, maybe.

One more Amstrad CPC 6128 plus revived. :-) :-) :-) :-)  :-) :-) :-) :-)  :-) :-) :-) :-)  :-) :-) :-) :-)  :-) :-) :-) :-)  :-) :-) :-) :-)

Still thanks for looking and kind regards! flufduff. (& Good Night :-)  )

So glad you got it working. Now that's one more person for the we need new carts camp.


Hi Flufduff and welcome to the forum. I hope using your new plus brings you the same joy as it did 30 years ago. There is alot to catch up on.  ;D

Hi Flufduff,
     congrats on getting it working. It was most likely dirt on the cartridge edge connector. Just to answer your other question. Yes, the CPC+ is a pure 5V design including the floppy drive. No 12V or anything else needed. Not sure what you mean with the second 7405 (Did you mean 7805?). If you mean the schematic below (which is in the Plus Service Manual), this is just for the GX4000. The 11V input is to supply the correct switching voltage to the SCART output. The second 7805 is so that the video circuitry has a completely isolated 5V supply to avoid noise in the picture.



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